Identify a specific scientific concept or phenomenon for which our understanding has changed over time (e. g., the nature and structure of the atom, genetics, plate tectonics, evolution, the solar system, big bang, biogeography).

The theory of plate tectonics evolved from the previous theory of continental drift. Alfred Wegener came up with the latter theory in comparing the coastline shapes of for example eastern South America with western Africa they seemed to fit together. However, there was no mechanism for this until I believe in the late 1960's or early 1970's the theory of plate tectonics was developed which the Canadian geophysicist played a part in J. Tuzo Wilson. The latter theory shows how the mid-oceanic ridges are spreading and the continental margins have the ocean floor subducting.